Kagame denounced the "direct role of Belgium and France in the political preparation for the genocide", in an interview with Jeune Afrique magazine to mark the 20th anniversary of the slaughter.
He also accused French soldiers who took part in a military humanitarian mission in the south of the former Belgian colony of being both accomplices and "actors" in the bloodbath.
Paris has repeatedly denied the accusations and insisted that French forces had striven to protect civilians.
Kagame's rebels overthrew the Hutu-dominated government but many alleged perpetrators of atrocities escaped.
A 2008 report by Rwanda's MUCYO commission of inquiry concluded that France had trained the militias that carried out killings and French troops had taken part in massacres.
It accused 13 politicians and 20 officers by name.
"Twenty years later, the only thing you can say against them (the French) in their eyes is they didn't do enough to save lives during the genocide," Kagame told Jeune Afrique. "That's a fact but it hides the main point: the direct role of Belgium and France in the political preparation of the genocide and the participation of the latter in its very execution."
Relations between Kigali and Paris were completely frozen from 2006 to 2009 but have improved recently.
Last month, in a landmark ruling, a French court sentenced former Rwandan army captain Pascal Simbikangwa to 25 years in prison for his role in the massacres.
French Justice Minister Christiane Taubira was set to attend commemorations of the massacres in Kigali on Monday.